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Interpretive Summary: Medusahead is an exotic annual grass invading vast expanses of western rangelands. However, resources are limited for managing this problem. Thus, information on where medusahead infestations are more common could be useful for prioritizing management. We compared medusahead invasion levels among roads, animal trails, and random locations. Medusahead was more abundant and had higher cover along roads than animal trails and random locations. Medusahead was also more abundant along animal trails than random locations. This suggests that medusahead is probably spreading more along roads and to a lesser extent along animal trails than at random locations. These results can be use by land managers to help prioritize where medusahead control treatments should be applied and where to monitor for new infestations.

Technical Abstract: Medusahead, an exotic annual grass, is rapidly spreading and causing ecological damage across the western United States. It is critical that land managers prioritize where they direct treatment and monitoring efforts due to the vast areas this exotic plant occupies and the limited amount of resources available for its management. Identifying where and by what means medusahead is spreading could provide valuable information to assist in determining where prevention and control efforts should be applied. We compared medusahead invasion levels along unimproved roads, animal trails, and random transects at six sites in southeastern Oregon to determine where medusahead was more common and identify potential vectors for its spread. Medusahead was more common and its cover was greater along unimproved roads than trails and random transects. Medusahead infestations were also larger along roads. Medusahead was more common along animal trails than random locations, but differences were less evident. Our results suggest that medusahead spreads along roads. This implies, though not conclusively, that vehicles may be one of the most important vectors for spreading medusahead. Our results also suggest that animals may be a vector for medusahead dispersal. However, medusahead invasions were much more concentrated near roads than trails suggesting that medusahead management along roads should be a higher priority. Medusahead invasion is not random across the landscape and thus, control and monitoring efforts can be prioritized based on potential vector pathways to manage this invasive plant.